Patent GB-1384570-A (GB)
Title: Method and machine for making thermoplastic bags
IPC: B31B23/00
Filed: 1972-11-10
Abstract: 1384570 Bag making machines; seaming non-metallic sheet material FMC CORP 10 Nov 1972 [12 Nov 1971] 51905/72 Headings B5D and B5K [Also in Divisions F2 and B8] In a machine for making bags from thermoplastic sheet material and which is basically as described in Specification 1,279,441, and which includes intermittently operable web feeding means, there is provided continually operable web feeding means to tension the web when the intermittently operable means is inactive and which conveys the cut bags away from the sealing and severing mechanism. Means is also provided to move the web in a direction opposite to the feed direction to cause stripping of the web from the sealing means. Each bag may or may not be provided with a skirt depending upon the closeness of the cutter to the seal. Web feed.-The web W is fed by feed rolls 40, 42 the lower roll being driven by belt 54 from a shaft 58. The feed is intermittent, the web being fed one bag length at a time. Shaft 58 is driven by a clutch-brake (64, Fig. 3, see also Headings F2E, F2C, F2L), comprising electrically energized brake and clutch coils and friction discs. Operation of a stop button energizes the brake and interrupts the drive to the web, also an actuator 114 is operated so that a rod 112 is extended to rotate the shaft 58 by 40 degrees in a reverse direction, and the leading edge of the web is withdrawn from the sealing and cutting area. The web feed, and also movement of the sealing and cutter members by means of rods 284, followers 152 and cams 150, is derived from a shaft 148 driven by a belt 262 from a main motor. A linkage, Fig. 7, consisting of a rod 266a, a gear segment 270 and gears 276, 280, 282 rotate a shaft 78 that is connected to the web feed shaft 58 via the clutch-brake means, a switch 260 controls the clutch-brake means as shaft 148 rotates so that the web is fed intermittently and also so that the web is stripped from the sealing bars when the gear segment turns in the reverse direction. Adjustment of the distance between centre 268 on the rod 266a and the centre of shaft 148 determines the amount the web is fed forward. Sealing and cutting bars.-These bars are reciprocated from cams 150 at each side of the machine and include tubular heating means and temperature control. The upper bar 122 is adjustable by studs 144 and nuts 146 and the lower bar 124 by studs 132 and nuts 134. Compressed air is delivered to the sealing area via a conduit 184 and valve 186, a rectangular chamber 188 has apertures directing the air tangentially over the web and the air also ensures that the web maintain its correct path to a stacking conveyer 32. The sealing bars are covered with glass fibre fabric impregnated with P.T.F.E. The fabric is mounted on a take-up roll so that an unused portion is presented to the upper sealing bar. Stacking conveyer.-The conveyer comprising belts 194, 196 carries away the completed bags and also maintains tension on the web immediately prior to the action of the cutters. After one bag length of web has been fed by rolls 40, 42 a cam 216 causes pick-off arms 200 to pivot about 211 so that the web is gripped by rolls 222, 248. The roll 222 is continuously rotated by a belt 224 and is engaged by the roll 248 mounted at the ends of the pick-off arms when the arms move down to tension the web back to the cutter. At the delivery end of the belts 194, 196 the bags are deposited on a stacking table.